The object of the present invention is the preparation of latexes of homo- and co-polymers of vinyl chloride: whose particles have a mean diameteI between 0.2 and 0.8 .mu.m and contain at least one organosoluble polymerization initiator, by the polymerization in microsuspension of the corresponding monomer or monomers. Its object likewise is the latexes resulting therefrom as well as their utilization, as seeding products, for the preparation in seeded microsuspension of homo- and co-polymers of vinyl chloride. The particles of said latexes contain all of the initiator necessary for the polymerization in seeded microsuspension and said polymerization does not require the complementary addition of polymerization initiator.
As used herein, the terms polymerization "in microsuspension" or "fine suspension" mean a polymerization in the presence of an organosoluble initiator or initiators of at least one monomer dispersed by agitation in an aqueous medium containing an emulsifying agent as a stabilizer.
French patent No. 1,485,547 shows for the preparation of vinyl chloride polymers by polymerization in seeded microsuspension, that it is known to use as seeding product a latex whose particles contain all of the initiator necessary for said polymerization.
The procedures, used until now, for the preparation of such a latex by polymerization n microsuspension present the following drawbacks:
(i) during the preparation of the dispersion of the monomer or monomers, which is carried out at a temperature generally between 10.degree. and 30.degree. C., almost always the formation of crusts is observed which disturb the functioning of the mechanical means employed and, on doing so, leads to a latex whose mean particle diameter is not reproducible from one operation to another, and/or PA1 (ii) durinq the polymerization of the monomer or monomers thus dispersed, the large quantity of initiator present, which can be equal to more than 20 times the quantity required for polymerization, frequently leads to sudden temperature elevations of the reaction medium, which can exceed and to the formation of large numbers of crusts.